Conductive, highly abrasion-resistant coatings, a process for their production and their use

ABSTRACT

Conductive, highly abrasion-resistant coatings on mouldings, consisting of at least one conductive layer and at least one highly abrasion-resistant layer, a process for their production and their use.

BACKGROUND

[0001] The invention relates to conductive, highly abrasion-resistantcoatings on mouldings, including at least one conductive layer and atleast one highly abrasion-resistant layer and a process for theirproduction and their use.

[0002] Conductive coatings based on polyethylene dioxythiophene (PEDT)already have a broad area of application, e.g, anti-static finishes forphotographic films. Numerous processes have described how suchconductive coatings can be produced. Basically, either the PEDT, whichis mixed with a binder, is applied or a multi-layered structure ischosen which has the advantage that binder and PEDT do not have to becompatible (miscible).

[0003] Conductive and scratch-resistant multi-layered structures forcoating picture tubes are described in WO 96/05606. Scratch-resistantlayers, for example silicon dioxide obtained by hydrolysis andcondensation of tetraethyl orthosilicate, are applied to a conductivePEDT layer, the layer thickness being limited to 50 to 250 nm.Alternatively, production of scratch-resistant layers frominorganic-organic hybrid materials is described, which layers can beapplied to the conductive layer in a layer thickness of 10 μm andgreater. These hybrid materials are based on trialkoxysilanes of FormulaR′—Si(OR)₃, wherein R′ represents a polymerisable group. Themulti-layered structures described in WO 96/05606 have severalfundamental disadvantages however:

[0004] After applying one of the described scratch-resistant layers, anotable level of conductivity can no longer be measured on the surfaceof the multi-layered structure.

[0005] Although a good level of scratch resistance is found (ascertainedby determining the lead pencil hardness), the abrasion resistance of thecoatings is poor.

[0006] High curing temperatures, 160° C. in the examples.

[0007] Antistatic multi-layered structures, in which the top(scratch-resistant) layer must also exhibit a certain level ofconductivity, or multi-layered structures with vitreous abrasionresistance cannot therefore be produced. Furthermore, curingtemperatures of 160° C. cannot be used for coating the majority ofplastics materials (softening).

[0008] Conductive coatings for transparent substrates, such as plasticsmaterials or glass for example, must retain their optical propertiesundiminished under mechanical load and must therefore have highresistance to abrasion. In WO 98/25274, mixtures are described whichproduce conductive coatings with good adhesion and with improved scratchresistance and transmittance of visible light. These mixtures consist ofa binder based on polyfunctional organosil(ox)anes and a conductiveorganic polymer which are known from WO 98/25274 and EP-A 0 947 520. Thedescribed binders are wherein they contain heterometals such as boron oraluminium and exhibit particularly good abrasion resistance.

[0009] In EP-A 0 947 520 it is stated that these binders reactsensitively to the addition of water, so by adding PEDT for example, inthe conventional form supplied (Baytron® P, approximately 1.3%dispersion of PEDT and polystyrene sulphonate in water), the processingtime of these mixtures is significantly reduced. Furthermore, theaddition of PEDT to the binder often leads to a loss in abrasionresistance which can clearly be seen even with highly abrasion resistantcoatings.

[0010] The object of the present invention was therefore to provideconductive surfaces provided with abrasion-resistant coatings, duringthe production of which the above-mentioned disadvantages are avoided.

[0011] Surprisingly it has now been found that a multi-layered structureon a substrate (moulding) including at least one conductive layer and atleast one highly abrasion-resistant layer still has a measurable levelof electrical conductivity on the surface of a moulding even though thetop, highly abrasion resistant layer is a good electrical insulator.

SUMMARY

[0012] The invention relates to a conductive and highlyabrasion-resistant coating. The coating comprises (a) a first layercomprising an electrically conductive polymer, and (b) a second layercomprising a highly abrasion-resistant layer of a polyfunctionalorganosil(ox)ane, wherein the coating is on a substrate of a multi-layerstructure. The invention also relates to a method for making and usingsuch a coating. These and other features, aspects, and advantages of thepresent invention will become better understood with reference to thefollowing description and appended claims.

DESCRIPTION

[0013] The present invention therefore relates to conductive and highlyabrasion-resistant coatings on a substrate as a result of amulti-layered structure, wherein an electrically conductive polymer isapplied in a first layer and a highly abrasion-resistant layer ofpolyfunctional organosil(ox)anes is applied in a second layer.

[0014] The mouldings coated according to the invention have a measurablelevel of electrical conductivity on the surface even though the highlyabrasion-resistant layer is a good insulator. The abrasion resistance ofthe multi-layered structure according to the invention (in the Taberabraser test) is similar to that of glass and curing can advantageouslytake place at temperatures lower than 160° C.

[0015] The present invention also relates to a process for producingconductive and highly abrasion-resistant coatings, wherein a conductivelayer is applied wet chemically in a first stage and a highlyabrasion-resistant layer is subsequently applied in a second stage.

[0016] Highly abrasion-resistant coatings in the context of theinvention are those which exhibit scattered light on the scratch mark(determined in accordance with ASTM D 1003) in the Taber abraser scratchtest (determined according to ASTM D 1044, 1,000 cycles, 500 g load perwheel, CS-10-F stones) of less than 20%, preferably less than 10%,particularly preferably less than 5%. In comparison, commerciallyavailable Makrolon®, for example, exhibits scattered light of more than30% on the scratch mark even after 100 cycles in the Taber abraser test.Glass exhibits scattered light of approximately 1 to 3% after 1,000cycles in the Taber abraser test.

[0017] Polyfunctional organosil(ox)anes in the context of the inventionare linear, branched or cyclic monomeric organosil(ox)anes which have atleast two silicon atoms with hydrolysable and/or condensationcrosslinking groups, wherein the silicon atoms are connected to oneanother in each case by means of a linking constructional unit with atleast one carbon atom. Examples of polyfunctional organosil(ox)anes arefound inter alia in EP-A 0 947 520. Production of aluminium- andboron-containing sol-gel condensates from which coatings withparticularly high abrasion resistance can be obtained is also describedtherein.

[0018] Sol-gel materials based on cyclic carbosiloxanes of Formula (I)

[0019] in which

[0020] m is 3 to 6, and preferably m is 3 or 4,

[0021] o is 2 to 10, and preferably o is 2 and

[0022] a is 1 to 3,

[0023] R¹ is C₁-C₆-alkyl, C₆-C₁₄-aryl, preferably R¹ is methyl, ethyl,isopropyl and when a is 1 R¹ can also represent hydrogen, furthermorewhen

[0024] R² is C₁-C₆-alkyl, C₆-C₁₄-aryl, preferably R² is methyl and

[0025] R³ is C₁-C₆-alkyl, C₆-C₁₄-aryl, preferably R³ is methyl, ethyland particularly preferably R³ is methyl,

[0026] are used to produce highly abrasion-resistant coatings which, inaddition to their high mechanical strength, also exhibit good weatheringresistance.

[0027] As described in WO 98/52992 and in U.S. Pat. No. 6,005,131, thecyclic carbosiloxanes are co-condensed with tetraalkoxysilanes,organotrialkoxysilanes and/or nanoparticles, the presence of aluminiumor boron alkoxides enhancing the abrasion resistance of the coatingsproduced from the condensates as shown in EP-A 0 947 520.

[0028] Conductive coatings in the context of the invention exhibit asurface resistance of 0.1 to 10¹² Ω/□.

[0029] Preparations of polythiophenes as they are described in DE-OS 4211 459, EP-A 339 340 and EP-A 440 957 are preferably used as conductivelayers. They contain polythiophene salts of the polythiophene^(m+)An^(m−)(^ polyanion) type, wherein the polythiophene cationpolythiophene^(m+) contains positively charged units of Formula (II).

[0030] wherein

[0031] A represents a C₁-C₄-alkylene radical optionally substituted byC₁-C₂₀-alkyl-, —CH₂—OH or C₆-C₁₄-aryl groups. The number of units in thepolythiophene cation can be between 5 and 100.

[0032] Examples of polyanions which can be used according to theinvention are the anions of polymeric carboxylic acids such aspolyacrylic acids, polymethacrylic acids, polymaleic acids, furthermoreanions of polymeric sulphonic acids such as polystyrene sulphonic acidsand polyvinyl sulphonic acids. These polycarbonic acids andpolysulphonic acids can also be copolymers of vinyl carboxylic acids andvinyl sulphonic acids with other polymerisable monomers such as acrylicacid esters and styrene.

[0033] The mean molecular weight M_(w) of the polymeric acids, fromwhich the polyanions which can be used according to the invention arederived, is 1,000 to 2,000,000, preferably 2,000 to 500,000. Thepolymeric acids or their alkali metal salts are commercially availableor can be produced by known processes as described, for example, inHouben-Weyl: “Methoden der organischen Chemie”, Volume E20,“Makromolekulare Stoffe”, Part 2, p. 1141 et seq.

[0034] With the multi-layered structure produced according to theinvention, a distinction has to be made between the conductivity of thePEDT-containing layer as such and the conductivity of the top, highlyabrasion-resistant coating. As the latter is an electrical insulator,the conductivity of the entire layer structure is obviously lower thanthat of the PEDT layer(s) beneath it.

[0035] The simplest layer structure produced according to the inventionconsists of the substrate, a PEDT-containing layer and a highlyabrasion-resistant top layer.

[0036] In an embodiment of the present invention, conductive andabrasion-resistant surfaces on mouldings are obtained in that aPEDT-containing layer is initially applied to the substrate and highlyvolatile constituents such as solvents are optionally evaporated. Thehighly abrasion-resistant coating is then applied with or withoutfurther curing and is finally cured by heat or irradiation.

[0037] In a further embodiment of the present invention, the surface ofthe substrate is treated chemically with an adhesion promoter, orphysically (plasma, corona), prior to application of the conductivelayer, in order to achieve improved adhesion. This is particularlyimportant with plastics materials but may also be necessary, forexample, with glass. It is, however, also possible to add the adhesionpromoter to the PEDT-containing solution, whereby an additional coatingstage can be avoided.

[0038] It is also possible to finally provide the multi-layeredstructure produced by wet chemistry according to the invention with aninorganic layer, for example, of SiO₂, TiO₂ or Al₂O₃ precipitated fromthe gaseous phase. As a result, the wear resistance or theanti-reflective effect can be further improved.

[0039] The conductive and highly abrasion-resistant layer can be appliedby any commonly known technique, such as centrifuging, spraying,dipping, casting, knife coating or brushing.

[0040] Examples of substrates which can be provided with themulti-layered structure according to the invention include metals,ceramics, wood, glass and plastics materials such as polycarbonate.

[0041] The surfaces produced according to the invention and providedwith a conductive and highly abrasion-resistant coating are used, e.g.,as low radiation screens (electrical resistance of the PEDT layer lessthan 1,000 Ω/□) or as antistatic and abrasion-resistant plasticsmaterials, for example, in the form of films, extruded parts orinjection mouldings. Polycarbonate, in particular, can be protected inthis way from mechanical damage and electrostatic charges.

[0042] The invention is further described in the following illustrativeexamples in all percentages are based on weight and on the totalquantity of all components used.

EXAMPLES

[0043] A mixture consisting of 42.92% Baytron® P, 2.58%N-methyl-2-pyrolidone, 0.86% Silquest® A 187 and 53.64% isopropanol wasused to produce the conductive layer (“CPP 105”). Baytron® P (Bayer AG,Leverkusen) is an approximately 1.3% dispersion of polyethylenedioxythiophene and polystyrene sulphonate in water.

[0044] Production of the Scratch-Resistant Coating I From Sol-GelSolution I

[0045] The scratch-resistant coating I was produced from the sol-gelsolution I consisting of 6.8% cyclo-{SiOCH₃[(CH₂)₂Si(CH₃)₂OH]}₄, 32.1%tetraethyl orthosilicate, 9.6% aluminium-2-butylate, 5.1% acetoaceticester, 12.6% 0.1 N aqueous toluene-p-sulphonic acid solution, 32.8%1-methoxy-2-propanol and 1% Tinuvin® 384. Production is described inEP-A 0 947 520.

[0046] Cyclo-{SiOCH₃[(CH₂)₂Si(CH₃)₂OH]}₄ was produced as described inU.S. Pat. No. 5,880,305.

[0047] Production of the scratch-resistant coating II from sol-gelsolution II The scratch-resistant coating II was produced from thesol-gel solution II which was produced as follows: initially, a mixtureof 12.7% cyclo-{SiOCH₃[(CH₂)₂Si(CH₃)(OEt)₂]}₄-oligomer, 26.6% tetraethylorthosilicate and 33.3% 1-methoxy-2-propanol was hydrolysed with 7.0%0.1 N aqueous toluene-p-sulphonic acid solution while stirring. After areaction time of 120 min., complex aluminium tributylate was added at 5°C. (produced by mixing 7.9% aluminium tri-sec-butylate in 2.6%1-methoxy-2-propanol with 4.2% acetoacetic ester at 0° C. whilestirring) and after stirring for a further 5 min. a further 4.8% 0.1 Naqueous toluene-p-sulphonic acid solution, 0.1% Tegoglide® 410 and 0.9%Tinuvin® 384 were added. After being heated to ambient temperature, thereaction mixture was finally stirred for a further 90 min. and was thenready for processing.

[0048] Cyclo-{SiOCH₃[(CH₂)₂Si(CH₃)(OEt)₂]}₄-oligomer was produced asdescribed in WO 98/52992.

[0049] The various layers were applied by centrifuging the maximum speed(in rpm) and the dwell time at maximum speed are always given (in s) ineach case.

[0050] The lead pencil hardness was determined to ASTM 3363, the wearresistance was tested by the Taber abraser test (ASTM D 1044; 1,000cycles, 500 g per wheel, CS-10-F stone) and subsequent determining ofthe scattered light (ASTM D 1003).

[0051] The surface resistance was determined with a commerciallyavailable measuring instrument (ITT, MX52S type) and conductive silverstrips arranged in a square (length of the strips=spacing between thestrips).

Example 1 Coating of Glass with Scratch-Resistant Coating I

[0052] The mixture CPP 105 was initially applied to six 7.5×7.5 cmsheets of glass by centrifuging and was cured for 1 hour at 130° C. Theprocess was repeated for a double coating. A 2 mm wide strip ofconductive silver was then applied over the entire length to twoopposing sides and was cured for 30 minutes at 160° C. After cooling,the electrical resistance was measured.

[0053] The above-described sol-gel mixture I was then also applied bycentrifuging (500 rpm, 20 s). The mixture was cured for 1 hour at 130°C. After cooling, both the surface resistance of the overall layerstructure and the electrical resistance of the conductive layer as suchwere determined. The abrasion resistance was ascertained by determiningthe lead pencil hardness.

[0054] The exact application conditions during centrifuging, theelectrical resistances measured and the results of the lead pencilhardness tests are summarised in Table 1. TABLE 1 Surface resistance[kΩ/□] Application conditions Scratch- Lead Sample conductive layer CPPCPP resistant pencil No. 105 105 coating I hardness 1 400 rpm, 20 s 2.8133 >9 H 2 2 × 400 rpm, 20 s 1.3 270  7 H 3 600 rpm, 20 s 3.6 notdetermined >9 H 4 2 × 600 rpm, 20 s 1.8  48 >9 H 5 1,000 rpm, 20 s 120not determined >9 H 6 2 × 1,000 rpm, 20 s 7.0  53 >9 H

Example 2 Coating of Makrolon® with Scratch-Resistant Coating I (withIntermediate Curing of the Conductive Layer)

[0055] A 10×10 cm sheet of Makrolon® was initially coated with3-amino-propyltrimethoxysilane by centrifuging (2,000 rpm, 20 s) andheat treated for 1 hour at 80° C. in order to improve adhesion. ThePEDT-containing mixture CPP 105 was then applied (1,000 rpm, 20 s) andsubsequently cured for 1 hour at 130° C. Finally, after cooling toambient temperature, the scratch-resistant coating I was applied (500rpm, 20 s) and was then cured for 1 hour at 80° C. and for 1 hour at130° C.

[0056] Measurement of the electrical resistances gave 1.4×10⁴ Ω/□ forthe conductive layer and 10⁸ Ω/□ on the surface of the scratch-resistantcoating I.

Example 3 Coating of Makrolon® with Scratch-Resistant Coating I (WithoutIntermediate Curing of the Conductive Layer)

[0057] Six 10×10 cm sheets of Makrolon® were initially coated with3-aminopyltrimethoxysilane by centrifuging (2,000 rpm, 20 s) and heattreated for 1 hour at 80° C. to improve adhesion. The PEDT-containingmixture CPP 105 was the applied and after evaporation for 10 min atambient temperature the scratch-resistant coating I was applied and wassubsequently cured for 1 hour at 80° C. and for 1 hour at 130° C. Theapplication conditions were varied for the PEDT-containing layer and thescratch-resistant paint I and are summarised in Table 2. The results ofthe Taber abraser test after determining the scattered light are alsolisted there. TABLE 2 Application Application conditions Surface Sampleconditions Scratch- Scattered resistance No. CPP 105 resistant paint Ilight^(*)) [Ω/□] 7 2,000 rpm, 400 rpm, 20 s 4.8 (0.7) 8.0 × 10⁸ 20 s 82,000 rpm, 500 rpm, 20 s 4.8 (0.8) 6.0 × 10⁸ 20 s 9 1,000 rpm, 400 rpm,20 s 4.7 (0.7) 2.0 × 10⁹ 20 s 10 1,000 rpm, 500 rpm, 20 s 5.3 (0.6) 1.3× 10⁹ 20 s 11 500 rpm, 400 rpm, 20 s 4.4 (0.8) 1.6 × 10⁹ 20 s 12 500rpm, 500 rpm, 20 s 4.6 (0.7) 1.0 × 10⁹ 20 s

Example 4 Coating of Glass with Scratch-Resistant Coating II

[0058] Initially, the mixture CPP 105 was applied to four 10×10 cmsheets of glass by centrifuging and was cured for 1 hour at 130° C. Theprocess was repeated for double or treble coatings. Subsequently, thesurface resistance of the coating applied in this way was determined.

[0059] The above-described sol-gel mixture II was subsequently appliedby centrifuging (500 rpm, 20 s). The mixture was cured for 1 hour at130° C. After cooling, the lead pencil hardness and the opticaltransmittance of the multi-layered structure obtained was determined.The results are summarised in Table 3. TABLE 3 Application conditionsconductive layer Surface CPP 105 resistance Lead Transmittance Samplescratch-resistant [Ω/□] pencil between 400 No. layer II CPP 105 hardnessand 700 nm 1 500 rpm, 20 s 5100 >7 H >84% 800 rpm, 20 s 2 500 rpm, 20 s5100 >7 H >86% 400 rpm, 20 s 3 2 × 500 rpm, 20 s 1900 >7 H >68% 400 rpm,20 s 4 3 × 500 rpm, 20 s  900 >7 H >51% 400 rpm, 20 s

Comparison example 1

[0060] A mixture of 10 mol % phenyltrimethoxysilane, 65 mol %3-glycidoxypropyltrimethoxylsilane, 5 mol % 3-aminopropyltriethoxysilaneand 20 mol % aluminium tributylate was produced as described in WO96/05606. In addition, 40 g aluminium tributylate were dissolved in 48 gisopropanol and reacted with 21 g acetoacetic ester. This mixture wasthen added to a mixture of 16 g phenyltrimethoxysilane, 120 g3-glycidoxypropyltrimethoxysilane and 9 g 3-aminopropyltriethoxysilane.The mixture was subsequently diluted with 100 g isopropanol and 100 gdiacetone alcohol and water was added while cooling with ice. After theadditions had been made, the reaction mixture was finally stirred for afurther 2 hours at ambient temperature. A 10×10 cm sheet of Makrolon®was initially coated with 3-aminopropyltrimethoxysilane by centrifuging(2,000 rpm, 20 s) and heat treated for 1 hour at 80° C. to improveadhesion. The above-described reaction mixture was then applied, also bycentrifuging (300 rpm, 20 s), and heat treated for 1 hour at 130° C.

[0061] A very low abrasion resistance was found in the Taber abrasertest (1,000 cycles). The scratch mark exhibited scattered light of morethan 38%.

What is claimed is:
 1. A conductive and highly abrasion-resistantcoating comprising: (a) a first layer comprising an electricallyconductive polymer, and (b) a second layer comprising a highlyabrasion-resistant layer of a polyfunctional organosil(ox)ane, whereinthe coating is on a substrate of a multi-layer structure.
 2. The coatingof claim 1, wherein the substrate is a moulding and the coating furthercomprises polyethylene dioxythiophene.
 3. The coating of claim 1,wherein the highly abrasion-resistant layer is produced from cycliccarbosiloxanes.
 4. The coating of claim 1, wherein the coating exhibitsless than 20% scattered light on the scratch mark in the Taber abraserscratch test.
 5. The coating of claim 1, wherein the coating exhibitsless than 10% scattered light on the scratch mark.
 6. The coating ofclaim 1, wherein the coating exhibits less than 5% scattered light onthe scratch mark.
 7. The coating of claim 1, wherein the coatingexhibits a surface resistance of 0.1 to 10¹² Ω/□.
 8. A process formaking a conductive and highly abrasion-resistant coating comprising aconductive and highly abrasion-resistant coating comprising (1) a firstlayer comprising an electrically conductive polymer, and (2) a secondlayer comprising an applied highly abrasion-resistant layer ofpolyfunctional organosil(ox)anes, wherein the coating is on a substrateof a multilayer structure, and wherein the process comprises: (a)applying the first layer wet chemically in a first stage on thesubstrate, and (b) subsequently applying the second layer in a secondstage.
 9. The process of claim 8, wherein a polyethylenedioxythiophene-containing layer is applied to the substrate in the firststage and highly volatile constituents comprising solvents, areoptionally evaporated.
 10. The process of claim 8, wherein the highlyabrasion-resistant coating is applied in the second stage and is curedby heat or irradiation.
 11. The process of claim 8, wherein thermalcuring takes place at temperatures lower than 160° C.
 12. The process ofclaim 8, wherein prior to the first stage, the surface of the substrateis chemically or physically treated.
 13. The coating of claim 1, whereinthe coating is a coating of a low radiation screen or an antistaticplastic material.
 14. The coating of claim 1, wherein the coating is acoating of a film, an extruded part or an injection moulding.